In a large bowl, whisk together the eggs, milk, salt, black pepper, and crushed red pepper flakes until well combined.
Heat a non-stick skillet over medium heat. Pour in the egg mixture and cook, stirring gently, until the eggs are just set but still slightly soft, about 3-4 minutes.
Remove the skillet from heat and stir in the cooked Italian sausage, mozzarella cheese, Parmesan cheese, and chopped parsley.
Lay out the flour tortillas on a clean surface. Divide the egg mixture evenly among the tortillas, placing it in the center of each.
Roll each tortilla tightly around the filling, folding in the sides as you go to secure the filling inside.
If desired, place the roll-ups seam-side down in the skillet over medium heat for 1-2 minutes to lightly toast the outside.
Slice each roll-up in half and serve warm.